Elevationally-extending strings of memory cells individually comprising a programmable charge storage transistor and methods of processing silicon nitride-comprising materials

ABSTRACT

A method comprises forming material to be etched over a substrate. An etch mask comprising a silicon nitride-comprising region is formed elevationally over the material. The etch mask comprises an elevationally-extending mask opening in the silicon nitride-comprising region that has a minimum horizontal open dimension that is greater in an elevationally-innermost portion of the region than in an elevationally-outermost portion of the region. The elevationally-outermost portion has a greater etch rate in at least one of HF and H3PO4 than does the elevationally-innermost portion. The etch mask is used as a mask while etching an elevationally-extending mask opening into the material. The silicon nitride-comprising region is exposed to at least one of HF and H3PO4 to increase the minimum horizontal open dimension in the elevationally-outermost portion to a greater degree than increase, if any, in the minimum horizontal open dimension in the elevationally-innermost portion. Other aspects and embodiments, including structure independent of method of manufacture, are disclosed.

RELATED PATENT DATA

This patent resulted from a continuation application of U.S. patentapplication Ser. No. 16/041,388, filed Jul. 20, 2018, entitled“Elevationally-Extending Strings Of Memory Cells Individually ComprisingA Programmable Charge Storage Transistor And Methods Of ProcessingSilicon Nitride-Comprising Materials”, naming Fei Wang, Tom J. John,Kunal Shrotri, Anish A. Khandekar, Aaron R. Wilson, John D. Hopkins, andDerek F. Lundberg as inventor, which was a continuation application ofU.S. patent application Ser. No. 15/851,532, filed Dec. 21, 2017,entitled “Elevationally-Extending Strings Of Memory Cells IndividuallyComprising A Programmable Charge Storage Transistor And Methods OfProcessing Silicon Nitride-Comprising Materials”, naming Fei Wang, TomJ. John, Kunal Shrotri, Anish A. Khandekar, Aaron R. Wilson, John D.Hopkins, and Derek F. Lundberg as inventors, now U.S. Pat. No.10,121,799, which was a divisional of U.S. patent application Ser. No.15/293,133 filed Oct. 13, 2016, entitled “Elevationally-ExtendingStrings Of Memory Cells Individually Comprising A Programmable ChargeStorage Transistor And Methods Of Processing Silicon Nitride-ComprisingMaterials”, naming Fei Wang, Tom J. John, Kunal Shrotri, Anish A.Khandekar, Aaron R. Wilson, John D. Hopkins, and Derek F. Lundberg asinventors, now U.S. Pat. No. 9,893,083, the disclosures of which areincorporated by reference.

TECHNICAL FIELD

Embodiments disclosed herein pertain to elevationally-extending stringsof memory cells individually comprising a programmable charge storagetransistor and to methods of processing silicon nitride-comprisingmaterials.

BACKGROUND

Memory provides data storage for electronic systems. Flash memory is onetype of memory, and has numerous uses in computers and other devices.For instance, personal computers may have BIOS stored on a flash memorychip. As another example, flash memory is used in solid state drives toreplace spinning hard drives. As yet another example, flash memory isused in wireless electronic devices as it enables manufacturers tosupport new communication protocols as they become standardized, and toprovide the ability to remotely upgrade the devices for improved orenhanced features.

A typical flash memory comprises a memory array that includes a largenumber of memory cells arranged in row and column fashion. The flashmemory may be erased and reprogrammed in blocks. NAND may be a basicarchitecture of flash memory. A NAND cell unit comprises at least oneselecting device coupled in series to a serial combination of memorycells (with the serial combination commonly being referred to as a NANDstring). Example NAND architecture is described in U.S. Pat. No.7,898,850.

Memory cell strings in flash or other memory may be arranged to extendhorizontally or vertically. Vertical memory cell strings reducehorizontal area of a substrate occupied by the memory cells incomparison to horizontally extending memory cell strings, albeittypically at the expense of increased vertical thickness.

Formation of vertically-extending strings of memory cells commonlyincludes etching of individual channel openings through multiplealternating tiers of material. Multiple materials are then depositedinto the channel openings, with the channel material being one of thelatter materials so-deposited. The channel material ideally electricallycouples with conductive or semiconductive material there-below.Accordingly, the respective materials first-deposited in the channelopening need to be removed from being centrally over the base of thechannel opening such that the channel material when it is deposited maymake electrical connection with the material at the base of the channelopenings. These earlier materials are typically so-removed by exposureto wet isotropic HF and/or H₃PO₄ etching. These earlier materials can bedifficult to remove from the base of the channel openings. This isparticularly so where a silicon nitride-comprising region atop thealternating materials through which the channel openings are formed hasless opening width at its elevationally-outermost surface than at itselevationally-innermost surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic sectional view of a substrate fragment inprocess in accordance with an embodiment of the invention.

FIG. 2 is a view of the FIG. 1 substrate at a processing step subsequentto that shown by FIG. 1.

FIG. 3 is a diagrammatic top plan view of the FIG. 2 substrate at aprocessing step subsequent to that shown by FIG. 2.

FIG. 4 is a view taken through line 4-4 in FIG. 3.

FIG. 5 is a view of the FIG. 4 substrate at a processing step subsequentto that shown by FIG. 4.

FIG. 6 is a view of the FIG. 5 substrate at a processing step subsequentto that shown by FIG. 5.

FIG. 7 is a graph diagrammatically representing etch rate andcomposition as a function of thickness position of a siliconnitride-comprising material in accordance with an embodiment of theinvention.

FIG. 8 is a graph diagrammatically representing etch rate andcomposition as a function of thickness position of a Si₃N₄-comprisingmaterial in accordance with an embodiment of the invention.

FIG. 9 is a graph diagrammatically representing etch rate andcomposition as a function of thickness position of a siliconnitride-comprising material in accordance with an embodiment of theinvention.

FIG. 10 is a graph diagrammatically representing etch rate andcomposition as a function of thickness position of a siliconnitride-comprising material in accordance with an embodiment of theinvention.

FIG. 11 is a graph diagrammatically representing etch rate andcomposition as a function of thickness position of a siliconnitride-comprising material in accordance with an embodiment of theinvention.

FIG. 12 is a graph diagrammatically representing etch rate andcomposition as a function of thickness position of a siliconnitride-comprising material in accordance with an embodiment of theinvention.

FIG. 13 is a view of the FIG. 6 substrate at a processing stepsubsequent to that shown by FIG. 6.

FIG. 14 is a view of the FIG. 13 substrate at a processing stepsubsequent to that shown by FIG. 13.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Embodiments of the invention include methods of processing siliconnitride-comprising materials. Such method embodiments are described withrespect to fabrication of an array of elevationally-extending strings ofmemory cells, although such may occur in processing any siliconnitride-comprising material regardless of resulting integrated circuitconstruction or resulting construction that may not include integratedcircuitry. Embodiments of the invention also includeelevationally-extending strings of memory cells independent of method ofmanufacture, with the memory cells individually comprising aprogrammable charge storage transistor. In this document,“elevationally-extending” and “extend(ing) elevationally” refer to adirection that is angled away by at least 45° from a primary surfacerelative to which a substrate is processed during fabrication and whichmay be considered to define a generally horizontal direction. Further,“vertical” and “horizontal” as used herein are generally perpendiculardirections relative one another independent of orientation of thesubstrate in three dimensional space. Further and unless otherwisestated, “elevational(ly)”, “higher”, “upper”, “lower”, “top”, “atop”,“bottom”, “above, “below”, “under”, “beneath”, “up”, and “down” aregenerally with reference to the vertical direction. Also,“elevationally-extending” and “extend(ing) elevationally” with respectto a field effect transistor are with reference to orientation of thetransistor's channel length along which current flows in operationbetween the source/drain regions.

Referring to FIG. 1, a substrate fragment or construction 10 may beconsidered as comprising a base substrate 12 that may include any one ormore of conductive/conductor/conducting (i.e., electrically herein),semiconductive, or insulative/insulator/insulating (i.e., electricallyherein) materials. Various materials are shown above base substrate 12.Materials may be aside, elevationally inward, or elevationally outwardof the FIG. 1-depicted materials. For example, other partially or whollyfabricated components of integrated circuitry may be provided somewhereabove, about, or within substrate 12. Control and/or other peripheralcircuitry for operating components within a memory array may also befabricated, and may or may not be wholly or partially within a memoryarray or sub-array. Further, multiple sub-arrays may also be fabricatedand operated independently, in tandem, or otherwise relative oneanother. As used in this document, a “sub-array” may also be consideredas an array. Regardless, any of the materials, regions, and structuresdescribed herein may be homogenous or non-homogenous, and regardless maybe continuous or discontinuous over any material which such overlie.Further, unless otherwise stated, each material may be formed using anysuitable or yet-to-be-developed technique, with atomic layer deposition,chemical vapor deposition, physical vapor deposition, epitaxial growth,diffusion doping, and ion implanting being examples.

Example substrate 12 comprises semiconductor material 17, for examplemonocrystalline silicon, having a conductively doped source material 19formed there-over or therein and which may comprise a portion ofcircuitry for the elevationally-extending strings of memory cells beingfabricated. An insulator 18 (e.g., doped or undoped silicon dioxideand/or silicon nitride) is shown elevationally between semiconductormaterial 17 and material 19. An example source material 19 isconductively doped polysilicon of 500 Angstroms thickness over anunderlying tungsten silicide of 900 Angstroms thickness. An examplethickness for insulator 18 is 2,000 to 5,000 Angstroms. In thisdocument, “thickness” by itself (no preceding directional adjective) isdefined as the mean straight-line distance through a given material orregion perpendicularly from a closest surface of an immediately adjacentmaterial of different composition or of an immediately adjacent region.Additionally, the various materials or regions described herein may beof substantially constant thickness or of variable thicknesses. If ofvariable thickness, thickness refers to average thickness unlessotherwise indicated, and such material or region will have some minimumthickness and some maximum thickness due to the thickness beingvariable. As used herein, “different composition” only requires thoseportions of two stated materials or regions that may be directly againstone another to be chemically and/or physically different, for example ifsuch materials or regions are not homogenous. If the two statedmaterials or regions are not directly against one another, “differentcomposition” only requires that those portions of the two statedmaterials or regions that are closest to one another be chemicallyand/or physically different if such materials or regions are nothomogenous. In this document, a material, region, or structure is“directly against” another when there is at least some physical touchingcontact of the stated materials, regions, or structures relative oneanother. In contrast, “over”, “on”, “adjacent”, “along”, and “against”not preceded by “directly” encompass “directly against” as well asconstruction where intervening material(s), region(s), or structure(s)result(s) in no physical touching contact of the stated materials,regions, or structures relative one another.

A stack 24 of material to be etched has been formed over substrate 12and comprises vertically-alternating tiers of control gate material 26and insulative material 28 (e.g., doped or undoped silicon dioxideand/or silicon nitride). Control gate material 26 is conductive, with anexample being conductively doped polysilicon. Example thicknesses foreach of materials 26 and 28 are 200 to 400 Angstroms, and such need notbe of the same respective thicknesses or of the same thickness relativeone another when materials 26 and 28 individually are of constantthickness. Material stack 24 is shown as having twelvevertically-alternating tiers, although fewer or likely many more (e.g.,dozens, hundreds, etc.) may be formed. The top layer of material 28 ofmaterial stack 24 may be made thicker or thinner than shown or analternate material provided there-over (not shown in FIG. 1) wheredesired as an etch-stop or polish-stop for better assuring a planarhorizontal substrate (if desired).

Referring to FIG. 2, an etch mask 25 has been formed elevationally overmaterial 24. Such as a minimum has a silicon nitride-comprising region32 that may comprise, consist essentially of, or consist of siliconnitride. In one embodiment, silicon nitride-comprising region 32 is in alower or lowest portion of etch mask 25, and in one embodiment as shownis directly against material 24. Example thickness for siliconnitride-comprising region 32 is 500 to 2,000 Angstroms, with 1,100Angstroms being a specific example. Etch mask 25 is shown as comprisinga hard masking material 30 (e.g., amorphous carbon) formed elevationallyover silicon nitride-comprising region 32. An example thickness formaterial 30 is 2,000 to 5,000 Angstroms. For purposes of the continuingdiscussion, silicon nitride-comprising region 32 may be considered ascomprising an elevationally-outermost surface 14 and anelevationally-innermost surface 16. Each is shown as being planar,although need not be so. Regardless, silicon nitride-comprising region32 has an elevationally-outermost portion having a greater etch rate inat least one of HF and H₃PO₄ than does an elevationally-innermostportion of silicon nitride-comprising region 32, and which is describedin more detail below.

Referring to FIGS. 3 and 4, elevationally-extending mask openings 20have been formed in etch mask 25. Only two such mask openings areformed, although likely hundreds, thousands, etc. would be formed forformation of hundreds, thousands, etc. of elevationally-extendingstrings of memory cells. The discussion proceeds relative to fabricationof a single mask opening 20 for fabrication of a singleelevationally-extending string of memory cells. In one embodiment, maskopening 20 is formed to be vertical or within 10° vertical. Exampletechniques for forming an opening 20 include dry anisotropic plasmaetching using lithography with or without pitch multiplication (e.g.,using photoresist and/or other imageable and/or non-imageablematerials). Mask opening 20 may be circular, ellipsoidal, rectangular,or of other shape in horizontal cross-section, with circular beingshown. Mask opening 20 in silicon nitride-comprising region 32 has aminimum horizontal open dimension 21 in an elevationally-innermostportion of region 32 that is greater than a minimum horizontal opendimension 22 in an elevationally-outermost portion of region 32. Suchmay form, for example, as an artifact in formation of mask opening 20 inregion 32. Mask opening 20 within silicon nitride-comprising region 32is shown as having a straight-linear taper between surfaces 14 and 16,although a curved, stepped, combination of straight and curved, etc. mayalternately occur or be provided. Mask opening 20 in hard mask material30 is shown as being of constant minimum horizontal open dimension 22although need not be so.

Referring to FIG. 5, etch mask 25 has been used as a mask while etchingan elevationally-extending opening 23 into material 24. In oneembodiment and as shown, opening 23 extends completely through material24 and partially into material 19. In one embodiment and as shown,opening 23 will comprise a channel opening in which at least channelmaterial will be formed of the programmable charge storage transistorsbeing formed. Opening 23 may have an example maximum horizontal opendimension (e.g., 21) of 850 to 1,250 Angstroms at itselevationally-outermost portion and which tapers (not shown) to ahorizontal open dimension of 5 percent to 10 percent less at itselevationally-innermost portion where meeting with source material 19.

Referring to FIG. 6, silicon nitride-comprising region 32 has beenexposed to at least one of HF and H₃PO₄ to increase horizontal opendimension 22 to dimension 22 z in the elevationally-outermost portionthereof to a greater degree than increase, if any, in minimum horizontalopen dimension 21 in the elevationally-innermost portion of siliconnitride-comprising region 32. In the depicted example embodiment, and byway of example only, such shows no increase in minimum horizontal opendimension 21 in the elevationally-innermost portion and increase of suchdimension in the elevationally-outermost portion to a dimension 22 zthat is equal to that of open dimension 21, although such may notso-perfectly occur. Masking material 30 (not shown) is shown as havingbeen removed, although such need not occur. Any such removal may occurprior to, after, and/or during exposure of region 32 to at least one ofHF and H₃PO₄. In one embodiment, however, such is removed prior toexposure of region 32 to at least one of HF and H₃PO₄. This will provideexposure of surface 14 of region 32 to the HF and/or H₃PO₄, and therebythickness of silicon nitride-comprising region 32 may be reduced (notshown). In one embodiment, the exposing is to HF, in one embodiment isto H₃PO₄, and in one embodiment is to both HF and H₃PO₄. Any suitableetching conditions and HF and/or H₃PO₄ concentrations may be used. Forexample and by way of example only, ambient temperature or elevatedtemperature of a liquid etching solution of volumetric ratio of 10:1 to1,000:1 water to one or both of HF and H₃PO₄ may be used.

Widening of opening 20 in the elevationally-outermost portion of siliconnitride-comprising material 32 may facilitate access of HF and/or H₃PO₄to subsequently deposited materials at the base of channel opening 23for removal of such materials before formation of the channel material.While the invention was motivated for this purpose in overcoming theproblem identified in the “Background” section above, the invention isin no way so-limited.

As stated above, silicon nitride-comprising region 32 is fabricated in amanner such that its elevationally-outermost portion has a greater etchrate in at least one of HF and H₃PO₄ than does itselevationally-innermost portion. Such may be achieved by any existing oryet-to-be-developed-manners, with three such example techniques beingdescribed below. Specifically, and in a first example and in oneembodiment, the elevationally-outermost portion of region 32 isfabricated to have greater intrinsic mechanical stress in the tensiledirection than does the elevationally-innermost portion. In oneembodiment, the elevationally-outermost portion is fabricated to haveintrinsic tensile mechanical stress (e.g., 500 to 1,000 mega-Pascals[mPa]), and in one embodiment the elevationally-innermost portion isfabricated to have intrinsic tensile mechanical stress (e.g., 350 to 850mPa) yet which is less than that of the elevationally-outermost portion.For example and by way of example only, an elevationally-outermostportion having on average greater intrinsic mechanical stress of atleast 150 mPa in the tensile direction in comparison to that of theelevationally-innermost portion may provide a suitable etch rate deltain HF and/or H₃PO₄.

Degree of tensile or compressive intrinsic mechanical stress in asilicon nitride-comprising region 32 may be determined or controlled byprocessing conditions during deposition. For example, consider PECVD ofsilicon nitride using the following conditions/parameters:

Process Parameters Parameter Range SiH₄ flow 100-300 sccm NH₃ flow300-1,000 sccm High frequency RF power 200-500 Watts Pressure 2-5 TorrElectrode-wafer spacing 400-1,000 millimeters Temperature 450°-500° C.With respect to the above parameters, each of less RF power, greaterpressure, and greater spacing achieves greater intrinsic mechanicalstress in the tensile direction. Accordingly with respect to the aboveexample, ideally, the elevationally-outermost portion of siliconnitride-comprising region 32 is fabricated using less RF power, greaterpressure, and greater spacing than is used in fabricating theelevationally-innermost portion of silicon nitride-comprising region 32.

In a second example and in one embodiment, and perhaps independent ofintrinsic mechanical stress at least to some degree, carbon contentwithin silicon nitride impacts etch rate within HF and H₃PO₄, withgreater carbon content resulting in less etch rate than lesser or nocarbon content. Accordingly and in one embodiment, theelevationally-outermost portion of silicon nitride-comprising region 32is fabricated to have less carbon content, if any, than theelevationally-innermost portion of region 32. In one embodiment, theelevationally-innermost portion has 0.5 to 9 atomic percent carbon, andin one such embodiment 0.5 to 2 atomic percent carbon. In oneembodiment, the elevationally-outermost portion has 0 to 0.001 atomicpercent carbon.

In a third example and in one embodiment, and perhaps independent ofintrinsic mechanical stress at least to some degree, boron contentwithin silicon nitride impacts etch rate in HF and H₃PO₄, with greaterboron content resulting in greater etch rate than lesser or no boroncontent. Accordingly and in one embodiment, the elevationally-innermostportion of silicon nitride-comprising region 32 is fabricated to haveless boron content, if any, than the elevationally-innermost portion ofregion 32. In one embodiment, the elevationally-outermost portion has 1to 20 atomic percent boron, and in one embodiment theelevationally-innermost portion has zero to 0.001 atomic percent boron.

Regardless of which one or more of the above three techniques, or othertechnique(s), is/are used to achieve an etch rate delta between anelevationally-outermost and elevationally-innermost portion, in oneembodiment the respective etch rate is constant elevationally throughone or both of the elevationally-outermost portion and theelevationally-innermost portion, and in one alternate embodiment isvariable elevationally through one or both of theelevationally-outermost portion and the elevationally-innermost portion.Regardless and in one embodiment, the difference in the etch rate in theelevationally-outermost and elevationally-innermost portions is along astepped gradient. For example and by way of example only, FIG. 7 showsetch rate and composition as a function of thickness position of siliconnitride-comprising region 32 along a stepped gradient 45. FIG. 7 showsincreasing etch rate of silicon nitride by exposure to at least one ofHF and H₃PO₄, over a set time period, from bottom surface 16 to topsurface 14 of a silicon nitride-comprising region 32 fabricated to havean elevationally-outermost portion have a greater such etch rate thandoes an elevationally-innermost portion. FIG. 7 shows but one exampleembodiment wherein an elevationally-outermost portion 34 is of the samethickness as an elevationally-innermost portion 36, with the “mid”portion of the x-axis of the graph depicting the middle of theelevational thickness of region 32. Such elevationally-outermost andelevationally-innermost regions may alternately have unequalthicknesses, for example either being larger than the other.

FIG. 7 also shows an embodiment wherein the depicted example etch rateis constant elevationally through each of elevationally-outermostportion 34 and elevationally-innermost portion 36. Such may beaccomplished, by way of example, by making the composition of region 32homogenous, but different, in each of regions 34 and 36 from surface 14,16, respectively, to the “mid” thickness location. Further, suchadditionally shows one example embodiment wherein difference in the etchrate between portion 34 and portion 36 is across at least one verticalstep wall 35 of stepped gradient 45. Additionally, FIG. 7 shows anexample embodiment wherein etch rate of elevationally-innermost portion36 is greater than zero, although such alternately could be essentiallyzero throughout the etching time period. Again, method of fabricationand/or the composition of regions 34 and 36 may be tailored to achieve adesired etch profile of region 32, for example as shown in FIG. 7.

FIG. 8 shows an example alternate embodiment by which region 32 may befabricated. Like numerals from the above-described embodiments have beenused where appropriate, with some differences being indicated with thesuffix “a”. FIG. 8 shows an embodiment wherein each of anelevationally-innermost portion 36 a and an elevationally-outermostportion 34 a along a stepped gradient 45 a has an etch rate which isvariable elevationally through each of elevationally-outermost portion34 a and elevationally-innermost portion 36 a, and having a non-verticalstep-wall 35 a. Such may be accomplished, by way of example, by makingthe composition of region 32 non-homogenous and different in each region34 and 36 to achieve the depicted etch rates at the different thicknesslocations.

FIG. 8 shows an example embodiment wherein the variability in etch rateis along a linear gradient that is straight-linear in each of portions34 a and 36 b. FIG. 9 shows an alternate example embodiment to that ofFIG. 8 wherein like numerals are used but for some differences beingindicated with the suffix “b”. In FIG. 9, the etch rate along a steppedgradient 45 b is shown as being variable elevationally through each ofelevationally-outermost portion 34 b and elevationally-innermost portion36 b along a linear gradient that is curved, and to or from a verticalstep wall 35 b. Alternate gradients may of course be used, for examplealong a stepped gradient in one or both of portions 34 b and 36 b (notshown). Further, any combination of the disclosed and shown features ofFIGS. 7-9 (and FIGS. 10-12 described below) may be used.

FIG. 10 shows another example embodiment for the fabrication of siliconnitride-comprising region 32. Like numerals from the above-describedembodiments have been used where appropriate, with some constructiondifferences being indicated with the suffix “c”. In FIG. 10, siliconnitride-comprising region 32 has been formed with outermost andinnermost portions 34 c and 36 c, respectively, collectively havingthree steps and two step walls 35 c in a stepped gradient 45 c betweenelevationally-outermost surface 14 and elevationally-innermost surface16.

The above example FIGS. 7-10 embodiments show difference in etch ratebetween the elevationally-outermost and elevationally-innermost portionsas being along a gradient that includes a step (i.e., being along astepped gradient) at least due to presence of step walls 35/35 a/35 b/35c. Alternately, difference in etch rate between theelevationally-outermost and elevationally-innermost portions may bealong a linear gradient (i.e., which is not a stepped gradient), forexample as shown by way of examples only in FIGS. 11 and 12. FIG. 11shows an embodiment wherein a linear gradient 45 d betweenelevationally-innermost surface 16 and elevationally-outermost surface14 is straight-linear, with FIG. 12 showing an example embodimentwherein a linear gradient 45 e is curved from elevationally-innermostsurface 16 to elevationally-outermost surface 14. Alternate degrees ofetch rate delta and/or degree of curvature may of course be used, and acombination of straight section(s) and linear section(s) (not shown) ingradients may be used, for example without such being a steppedgradient.

Referring to FIG. 13 and in one embodiment, control gate material 26 hasbeen subjected an anisotropic wet etch to laterally recess it relativeto the original sidewalls of channel opening 23. Such an etch may beconducted selectively relative to materials 28, 32, and 19. In thisdocument, a selective etch or removal is where one material is removedrelative to another stated material at a rate of at least 2:1.

Referring to FIG. 14, several acts of processing have occurred relativeto FIG. 12. Specifically, control gate blocking insulator 40 (e.g., oneor more of silicon nitride, silicon dioxide, hafnium oxide, zirconiumoxide, etc.), programmable charge storage material 42 (e.g., materialsuitable for utilization in floating gates or charge-trappingstructures, such as, for example, one or more of silicon, siliconnitride, nanodots, etc.), and tunnel insulator 44 (e.g., one or more ofsilicon dioxide and silicon nitride), and channel material 50 have beensequentially formed in channel opening 23. Such are shown as having beensubjected to an etch (e.g., wet isotropic etch by exposure to at leastone of HF and H₃PO₄ or by an anisotropic etch) to remove such from beingsubstantially over horizontal surfaces before deposition of the nextsubsequent layer. Alternately and by way of example only, such may besubjected to such etching after deposition of two or more such layers,where for example a goal is for a subsequently deposited channelmaterial to electrically couple with source material 19. Regardless, andin one embodiment, silicon nitride-comprising region 32 has been exposedto at least one of HF and H₃PO₄ at least before forming control gateblocking insulator 40 to preclude it from shielding sidewalls of theelevationally-outermost portion of region 32 within opening 20 toexposure to such at least one of HF and H₃PO₄.

Regardless, channel material 50 and a dielectric material 52 (e.g.,silicon nitride and/or doped or undoped silicon dioxide) have beenformed to fill remaining volume of channel opening 23, followed byplanarizing materials 50 and 52 back at least to anelevationally-outermost surface of silicon nitride-comprising region 32.Accordingly, channel material 50 is shown as comprising a channel pillarin channel opening 23 in the form of a hollow channel pillar internallyfilled with dielectric material 52. Alternately, channel material 50 mayextend completely diametrically across channel opening 23 (e.g., nointernal dielectric material 52 and not shown) thereby forming anon-hollow channel pillar. Regardless, channel material 50 ideallycomprises doped semiconductive material (e.g., polysilicon) havingchannel conductivity-modifying dopant(s) present in a quantity thatproduces intrinsic semiconductor properties enabling the channelmaterial to operably function as switchable “on” and “off” channels forthe individual memory cells for control gate voltage above and below,respectively, a suitable threshold voltage (V_(t)) depending onprogramming state of the charge storage transistor for the respectiveindividual memory cell. An example such dopant quantity is 5×10¹⁷atoms/cm³ to 5×10¹⁸ atoms/cm³. Channel material 50 may be p-type orn-type.

FIG. 14 shows formation of elevationally-extending strings 80 ofindividual memory cells 88. Construction 10 is shown as comprising asingle memory cell 88 about the channel pillar in each tier of theelevationally-extending strings of memory cells. Alternately, and by wayof example only, any existing or yet-to-be-developed construction may beused wherein two or more memory cells are circumferentially spaced aboutthe channel pillar in a single tier in a given string (not shown).Regardless, example memory cells 88 comprise a programmable chargestorage transistor comprising materials 50, 44, 42, 40, and 26, and inone embodiment as shown extend elevationally.

The above-described processing was by way of example with respect toso-called “gate first” processing in comparison to so-called “gate last”or “replacement gate” processing. However, gate last/replacement gateprocessing may be used whereby a FIG. 1-starting-construction may bewith a material 24 comprising alternating tiers of different compositioninsulating materials (i.e., no control gate material 26 yet) with one ofsuch insulating materials being replaced with control gate material 26after forming the control gate blocking insulator, the programmablecharge storage material, the tunnel insulator, and the channel materialin channel opening 23. However as referred to above, processing inaccordance with the invention may occur with respect to a siliconnitride-comprising material regardless of resulting integrated circuitconstruction, and may occur where the resulting construction does notinclude integrated circuitry.

Embodiments of the invention encompass an elevationally-extending stringof memory cells individually comprising a programmable charge storagetransistor independent of method of manufacture. Nevertheless, any suchstring of memory cells may include any of the structural aspectsdescribed above with respect to method embodiments. Embodiments ofelevationally-extending strings (e.g., 80) of memory cells (e.g., 88)individually comprising a programmable charge storage transistor (e.g.,encompassed by materials 50, 44, 42, 40, and 26 in an individual tier)in accordance with structure embodiments of the invention may comprisevertically-alternating tiers of insulative material (e.g., 28) andcontrol gate material (e.g., 26). A channel pillar (e.g., material 50)extends elevationally through multiple of the vertically-alternatingtiers and comprises a projecting portion (e.g., 90 in FIG. 14) extendingelevationally outward of the elevationally-outermost tier of controlgate material. Tunnel insulator (e.g., 44), programmable charge storagematerial (e.g., 42), and control gate blocking insulator (e.g., 40) arebetween the channel pillar and the control gate material of individualof the tiers of the control gate material. A silicon nitride-comprisingregion (e.g., 32) encircles at least some of the projecting portion ofthe channel pillar (e.g., that portion of projecting portion 90 that isabove elevationally-outmost insulating material 28 as shown).

In one embodiment, the encircling silicon nitride-comprising materialcomprises an elevationally-outermost portion (e.g., 34/34 a/34 b/34 c/34d/34 e) and an elevationally-innermost portion (e.g., 36/36 a/36 b/36c/36 d/36 e). The elevationally-outermost portion has greater intrinsicmechanical stress in the tensile direction than does theelevationally-innermost portion. In one embodiment, the intrinsicmechanical stress is constant elevationally through one or both of theelevationally-outermost portion and elevationally-innermost portion, andin one embodiment is variable elevationally through one or both of theelevationally-outermost portion and elevationally-innermost portion. Inone embodiment, the elevationally-outermost portion has intrinsicmechanical stress, and in one embodiment the elevationally-innermostportion has intrinsic tensile mechanical stress. Any other attribute(s)or aspect(s) as shown and/or described above may be used.

In one embodiment, the encircling silicon nitride-comprising materialcomprises an elevationally-innermost portion comprising carbon, andcomprises an elevationally-outermost portion having less carbon content,if any, than the elevationally-innermost portion. In one embodiment, thecarbon content is constant elevationally through one or bothelevationally-outermost portion and the elevationally-innermost portion,and in one embodiment is variable elevationally through one or bothelevationally-outermost portion and the elevationally-innermost portion.In one embodiment, the elevationally-innermost portion has 0.5 to 9atomic percent carbon in one embodiment 0.5 to 2 atomic percent carbon,and in one embodiment 0 to 0.001 atomic percent carbon. In oneembodiment, the difference in said carbon content is along a steppedgradient, and in one embodiment along a linear gradient. Any otherattribute(s) or aspect(s) as shown and/or described above may be used.

In one embodiment, the encircling silicon nitride-comprising materialcomprises an elevationally-outermost portion comprising boron and anelevationally-innermost portion having less boron content, if any, thanthe elevationally-outermost portion. In one embodiment, the boroncontent is constant elevationally through the elevationally-outermostportion and the elevationally-innermost portion, and in one embodimentis variable through such portions. In one embodiment, theelevationally-outermost portion has 1 to 20 atomic percent boron, and inone embodiment 0 to 0.1 atomic percent boron. In one embodiment,difference in boron content between the elevationally-outermost andelevationally-innermost regions is along a stepped gradient, and in oneembodiment is along a linear gradient. Any other attribute(s) oraspect(s) as shown and/or described above may be used.

CONCLUSION

In some embodiments, a method comprises forming material to be etchedover a substrate. An etch mask comprising a silicon nitride-comprisingregion is formed elevationally over the material. The etch maskcomprises an elevationally-extending mask opening in the siliconnitride-comprising region that has a minimum horizontal open dimensionthat is greater in an elevationally-innermost portion of the region thanin an elevationally-outermost portion of the region. Theelevationally-outermost portion has a greater etch rate in at least oneof HF and H₃PO₄ than does the elevationally-innermost portion. The etchmask is used as a mask while etching an elevationally-extending maskopening into the material. The silicon nitride-comprising region isexposed to at least one of HF and H₃PO₄ to increase the minimumhorizontal open dimension in the elevationally-outermost portion to agreater degree than increase, if any, in the minimum horizontal opendimension in the elevationally-innermost portion.

In some embodiments, an elevationally-extending string of memory cellsindividually comprising a programmable charge storage transistorcomprises vertically-alternating tiers of insulative material andcontrol gate material. A channel pillar extends elevationally throughmultiple of the vertically-alternating tiers and comprises a projectingportion extending elevationally outward of the elevationally-outermosttier of control gate material. Tunnel insulator, programmable chargestorage material, and control gate blocking insulator is between thechannel pillar and the control gate material of individual of the tiersof the control gate material. Silicon nitride-comprising materialencircles at least some of the projecting portion of the channel pillar.The encircling silicon nitride-comprising material comprises anelevationally-outermost portion and an elevationally-innermost portion.The elevationally-outermost portion has greater intrinsic mechanicalstress in the tensile direction than does the elevationally-innermostportion.

In some embodiments, an elevationally-extending string of memory cellsindividually comprising a programmable charge storage transistorcomprises vertically-alternating tiers of insulative material andcontrol gate material. A channel pillar extends elevationally throughmultiple of the vertically-alternating tiers and comprises a projectingportion extending elevationally outward of the elevationally-outermosttier of control gate material. Tunnel insulator, programmable chargestorage material, and control gate blocking insulator is between thechannel pillar and the control gate material of individual of the tiersof the control gate material. Silicon nitride-comprising materialencircles at least some of the projecting portion of the channel pillar.In some embodiments, the encircling silicon nitride-comprising materialcomprises an elevationally-innermost portion comprising carbon and anelevationally-outermost portion having less carbon content, if any, thanthe elevationally-innermost portion. In some embodiments, the encirclingsilicon nitride-comprising material comprises an elevationally-outermostportion comprising boron and an elevationally-innermost portion havingless boron content, if any, than the elevationally-outermost portion.

In compliance with the statute, the subject matter disclosed herein hasbeen described in language more or less specific as to structural andmethodical features. It is to be understood, however, that the claimsare not limited to the specific features shown and described, since themeans herein disclosed comprise example embodiments. The claims are thusto be afforded full scope as literally worded, and to be appropriatelyinterpreted in accordance with the doctrine of equivalents.

The invention claimed is:
 1. An elevationally-extending string of memorycells individually comprising a programmable charge storage transistor,comprising: vertically-alternating tiers of insulative material andcontrol gate material; a channel pillar extending elevationally throughmultiple of the vertically-alternating tiers and comprising a projectingportion extending elevationally outward of the elevationally-outermosttier of control gate material; tunnel insulator, programmable chargestorage material, and control gate blocking insulator between thechannel pillar and the control gate material of individual of the tiersof the control gate material; and silicon nitride-comprising materialencircling at least some of the projecting portion of the channelpillar, the encircling silicon nitride-comprising material comprising anelevationally-outermost portion and an elevationally-innermost portion,the elevationally-outermost portion having greater intrinsic mechanicalstress in the tensile direction than does the elevationally-innermostportion, the elevationally-outermost portion and theelevationally-innermost portion being directly against one another anddifference in said intrinsic mechanical stress being along a steppedgradient.
 2. The string of memory cells of claim 1 wherein saidintrinsic mechanical stress is constant elevationally through each ofthe elevationally-outermost portion and the elevationally-innermostportion.
 3. The string of memory cells of claim 1 wherein theelevationally-outermost portion has intrinsic tensile mechanical stress.4. The string of memory cells of claim 3 wherein theelevationally-innermost portion has intrinsic tensile mechanical stress.5. An elevationally-extending string of memory cells individuallycomprising a programmable charge storage transistor, comprising:vertically-alternating tiers of insulative material and control gatematerial; a channel pillar extending elevationally through multiple ofthe vertically-alternating tiers and comprising a projecting portionextending elevationally outward of the elevationally-outermost tier ofcontrol gate material; tunnel insulator, programmable charge storagematerial, and control gate blocking insulator between the channel pillarand the control gate material of individual of the tiers of the controlgate material; and silicon nitride-comprising material encircling atleast some of the projecting portion of the channel pillar, theencircling silicon nitride-comprising material comprising anelevationally-innermost portion comprising carbon, the encirclingsilicon nitride-comprising material comprising anelevationally-outermost portion having less carbon content, if any, thanthe elevationally-innermost portion, the elevationally-outermost portionand the elevationally-innermost portion being directly against oneanother and difference in said carbon content being along a steppedgradient.
 6. The string of memory cells of claim 5 wherein said carboncontent is constant elevationally through each of theelevationally-outermost portion and the elevationally-innermost portion.7. The string of memory cells of claim 5 wherein theelevationally-innermost portion has 0.5 to 9 atomic percent carbon. 8.The string of memory cells of claim 7 wherein theelevationally-innermost portion has 0.5 to 2 atomic percent carbon. 9.The string of memory cells of claim 5 wherein theelevationally-outermost portion has zero to 0.001 atomic percent carbon.10. An elevationally-extending string of memory cells individuallycomprising a programmable charge storage transistor, comprising:vertically-alternating tiers of insulative material and control gatematerial; a channel pillar extending elevationally through multiple ofthe vertically-alternating tiers and comprising a projecting portionextending elevationally outward of the elevationally-outermost tier ofcontrol gate material; tunnel insulator, programmable charge storagematerial, and control gate blocking insulator between the channel pillarand the control gate material of individual of the tiers of the controlgate material; and silicon nitride-comprising material encircling atleast some of the projecting portion of the channel pillar, theencircling silicon nitride-comprising material comprising anelevationally-outermost portion and an elevationally-innermost portion,the elevationally-outermost portion comprising at least two of (a), (b),and (c), where, (a) greater intrinsic mechanical stress in the tensiledirection than the elevationally-innermost portion; (b) less carboncontent, if any, than the elevationally-innermost portion; and (c) moreboron content than in the elevationally-innermost portion, if any in theelevationally-innermost portion.
 11. The string of memory cells of claim10 wherein the elevationally-outermost portion comprises all of (a),(b), and (c).